I was reminded during our investigation of the self-proclaimed ‘church’ which prescribes bleach for almost every illness that sometimes the most harmful people are those convinced of their own righteousness. Members of this sect have been promoting two chemicals which when combined form bleach. This mixture, they claim, could cure (or ‘purge’) everything from autism to Alzheimer’s to aids – and a host of ailments in between.

The reaction of many to this piece has been to assume that it’s nothing more than a money-making ploy; preying upon desperate people for financial gain. But during our secret filming operation I became convinced the adherents believe every word they say.

Neither myself nor my colleagues are medical experts. For all we knew this time last month, bleach really does cure autism. So we sought an extremely wide range of independent medical and scientific opinion on the so-called ‘miracle solution’. This included (but was not limited to), a leading autism charity, a world autism expert at University College London, a leading GP, experts at the Department of Health and an independent public laboratory. All were unanimous: there is not a shred of evidence this stuff works, but it does carry a considerable risk of harm. Supporters maintain that the white matter excreted by patients taking it either orally or as an enema is the ‘parasite’ causing the illness. In reality (and if you are squeamish, please do not read the rest of this sentence) this is likely to be part of the digestive system of the person who has imbibed the bleach.

But the tone of one supportive Facebook page last night continued to reflect the unshakeable belief in this ‘cure’ among the Reverend we featured and his supporters. “I don’t go down the path of fear,” he wrote. “I stand in truth.”

The many journalists and independent experts involved in this investigation were castigated as propagandists. Our team was described by one commentator using a certain word of Anglo-Saxon origin, which sounds rather like the name of the King Canute, and also its Danish spelling, Knut.

But there is no holding back the tide of scientific opinion on this one.

Clearly, there are questions to be asked about the existing system of regulation when it comes to this ‘treatment’. Can it be right that Trading Standards (and therefore ultimately the Department of Business, Innovation and Skills) is the regulator? Would it not be better for the MHRA to take it on, meaning that the backstop was the Department of Health, with its many experts in cancer care and autism? That way there would be a national strategy, rather than enforcement that varies from county to county.

But whether or not the authorities do more to get to grips with all this, one thing is for sure. Self-deception and placebo, nurtured in the echo box of social media and conferences where only like-minded people may attend, are a formidable force indeed.

I can’t remember working on another investigation like it.

The Reverend has made no comment to us. The church insists its treatment is a ‘sacrament’ that is ‘no different to bread and wine at a church service’ and pointed out that even table salt can be deadly if too much is ingested.